ABSTRACT: Betalactam allergy remains the most common drug allergy. There are a large number of patients labelled as allergic without having been studied. This creates a major health resource problem, having to use alternative antibiotics that can increase medical costs, patient morbidity, and potentially contribute to further antibiotic resistance. We performed a descriptive epidemiological study in two population areas of allergy to beta-lactam antibiotics, which serve to determine the actual incidence of true allergic and obtain quantitative results with which to optimize current diagnostic protocols. According the findings, the importance of diagnosing beta-lactam allergy is confirmed. The most efficient diagnostic test is the intradermal. In case of negative skin tests, it is necessary to perform a provocation with the drug involved for a conclusive diagnosis. The retest should be conducted in pediatric cases with severe reactions and negative initial study. In our work, advancing age is not influential in beta-lactam allergy.